The invention relates to wireless audio microphone systems.
In order to provide audio communication between a talker and those listening to the talker, audio electronic equipment is often utilized to facilitate the communication. The term xe2x80x9ctalkerxe2x80x9d can connote a variety of input sources, including a person articulating language or a musical band playing a song. Moreover, the talker may require an untethered connection to the audio electronic equipment for greater mobility. A wireless connection between the acoustical speaker and the electronics equipment can be provided by frequency (FM) radio techniques in which the audio electronics equipment comprises a transmitter (which includes an encoder) and a receiver (which includes an decoder). In such an arrangement, the transmitter processes the audio signal as provided by the talker and modulates the signal so that the transformed signal can be conveyed over the wireless path to a receiver. The receiver demodulates the received signal, and the processed received signal is then presented to circuitry that may amplify the processed received signal. The corresponding signal may be recorded by additional recording circuitry or may be converted into an audio signal with an acoustical speaker arrangement.
The quality of the processed received signal, and consequently the associated audio signal, can be degraded by any xe2x80x9cnoisexe2x80x9d that is generated in the wireless path between the encoder and the decoder. (The term xe2x80x9cnoisexe2x80x9d is associated with a randomly varying signal superimposed on the desired, undistorted signal). There are a number of sources of noise with respect to the wireless path, including transmitter VCO (voltage controlled oscillator) phase noise, transmitter synthesizer stability, the quality of the FM detector in the receiver, receiver RF band pass filtering, and the receiver""s local oscillator. Moreover, with FM radio techniques the wireless path is susceptible to FM noise generated when a weak radio signal as received by the receiver.
The FM noise results in the audio signal (as provided to the listener) having xe2x80x9cbreathingxe2x80x9d characteristics because of the similar sound characteristics of someone breathing. The xe2x80x9cbreathingxe2x80x9d effect is caused by the dynamic noise in conjunction with the type of companding. Moreover, the degree of the xe2x80x9cbreathingxe2x80x9d effect increases with the dynamic noise level. The resulting effect can be noticeable to the listener and is perceived as a degradation of the audio signal. Thus, a solution that ameliorates the xe2x80x9cbreathingxe2x80x9d effect is an advancement in wireless microphone technology.
The present invention mitigates the xe2x80x9cbreathing effectxe2x80x9d associated with a wireless communications path between an encoder and a decoder of a wireless audio noise reduction system. Otherwise, the listener perceives a sound that is characteristic of someone breathing. The xe2x80x9cbreathingxe2x80x9d effect is caused by the dynamic noise in conjunction with the type of companding. Moreover, the degree of the xe2x80x9cbreathingxe2x80x9d effect increases with dynamic noise level.
The present invention provides apparatus and method to mitigate the corresponding breathing effect. According to the present invention, the wireless audio noise reduction system comprises an encoder and a decoder. The encoder comprises a variable compressor that invokes compression whenever the input signal is above a first input threshold, a frequency modulation (FM) modulator, and a matching network that interfaces the modulator to a first antenna that transmits over the wireless communications path. The decoder receives a signal from the encoder over the wireless communications path through a second antenna. The decoder comprises a FM detector and a variable expander that invokes expanding operation above a second input threshold.
An exemplary embodiment of the present invention is presented illustrating an architecture of the encoder and decoder having a communications path such as a radio path or a cable. Moreover, an electrical design of the encoder and decoder is presented with commercially available components.